Field of the Invention
The present invention relates to an image forming apparatus which performs a transfer output control at the time of forming an image.
Description of the Related Art
In recent years, in an image forming apparatus, for example, a copying machine or a laser beam printer, in order to obtain a high quality image even in a case where the environment of the installation site thereof is changed, various controls have been performed in the image forming process. For example, in a case where a high voltage is applied to an image forming component, abnormal discharge may occur according to the environment (temperature and humidity). Since the occurrence of the abnormal discharge greatly influences good or bad image quality, the occurrence of the abnormal discharge is prevented by changing the image forming condition according to the above-described factors.
As the control performed in the related art, there is ATVC (Active Transfer Voltage Control) of applying a constant current to a transfer roller which is to be applied with a high voltage before image formation and performing application of a constant voltage at the time of image formation by using a voltage value applied to the constant current circuit. This control copes with a change in resistance of the transfer roller according to a change of the environment.
However, this control method does not cope with a change in atmospheric pressure. Therefore, for example, when the apparatus is used at a high-altitude area where the atmospheric pressure is low, the image may be abnormal. When high voltages are applied to a transfer unit and a separation charge removal unit having different application polarity at a high altitude based on only the environment condition of temperature and humidity, leakage as abnormal discharge occurs between the two components (in a gap). Accordingly, deterioration in image quality occurs due to a shortage of a transfer current or the like, or damage to an electric element on a board occurs due to a flow of an excessive current according to the leakage.
The relationship between a leakage occurrence voltage and atmospheric pressure is known as the Paschen's law. In a case where the gap is maintained constant, a discharge starting voltage is decreased as the atmospheric pressure becomes low, and the abnormal discharge such as leakage easily occurs as the altitude become high.
With respect to the abnormal discharge, for example, Japanese Patent Laid-Open No. 5-88434 discloses an apparatus where an atmospheric pressure detection sensor is provided to an image forming apparatus and a control device changes an image forming condition according to an output of the sensor.
In addition, Japanese Patent Laid-Open No. 2010-48960 discloses an apparatus where, without providing an atmospheric pressure detection sensor, a dedicated leakage detection circuit which detects a leakage current occurring at the time of applying a high voltage is provided to a high-voltage applying unit which applies a high voltage to a transfer unit to detect the leakage current occurring in the state where the atmospheric pressure is low and to change an image forming condition.
However, in the image forming apparatus disclosed in Japanese Patent Laid-Open No. 5-88434, an atmospheric pressure sensor needs to be newly installed. In addition, even in the atmospheric pressure condition that the leakage easily occurs due to a low atmospheric pressure, under a high-temperature high-humidity environment condition where a resistance value of an object which a high voltage is to be applied is decreased, the voltage may not reach the leakage occurrence voltage. Even in a case where there is no need to decrease the applied voltage, the control of decreasing the applied voltage is performed based on only the atmospheric pressure condition, so that deterioration in image quality may occur due to a shortage of the transfer current.
In addition, in the image forming apparatus disclosed in Japanese Patent Laid-Open No. 2010-48960, since the leakage detection circuit is configured by arranging dedicated patterns for leakage detection with slight narrow spacing in high-voltage output lines in a high-voltage power supply board, it is not possible to accurately detect whether or not the leakage occurs between image forming components where the leakage actually occurs.